A spectrum analyzer is conventionally known which measures a frequency characteristic of an input signal by performing frequency sweep (see, for example, Patent Document 1). The spectrum analyzer has input terminals in two lines and measures a frequency characteristic of a signal input through one of the input terminals. The measured frequency characteristic is displayed through a display section.    Patent Document 1: Japanese Patent Laid-Open No. 8-233875 (pp. 3-4, FIGS. 1-2)